This is higher in London (£47,546), the South East (£32,664), the East of England (£29,128) and the South West (£25,976).
Tarquin Purdie, founder and chief executive at HaMuch.com, said: “Knotweed is a homeowner’s worst nightmare and there really is no DIY fix for this aggressive backyard vandal.
“It can take months on end to ensure it has been properly disposed of but can be more costly should you decide to turn a blind eye.
“The quicker you can get on top of the problem, the better, as a house with knotweed will not only drop in value but will also struggle to find a buyer.”
It’s believed that at least 5% of homes across the UK are affected by knotweed.
With 29 million homes across the nation, that equates to over 1.4 million properties impacted and £34.12bn wiped off in value.
With the highest house prices, homeowners in Kensington and Chelsea stand to lose £119,162 on the price of their property if they find it has been infested with knotweed.
Westminster and Camden are the next largest price losses, facing a loss £93,860 and £86,280 respectively.
